The present invention relates to an improved process of producing secondary and tertiary amino-functional silanes, and to the novel silyl imines, silyl imides, and secondary and tertiary amino-functional silanes produced therefrom.
Amino silanes are commonly used as adhesion promoters in adhesives and sealants, and as coupling agents in compositions used in the plastics and glass-fibers industries and in foundries, in fabric treatment compositions, and in personal care products.
In particular, secondary and tertiary amino functionalized silanes are useful as coupling agents in the fiberglass and automotive glass industries. Currently the best technology for producing functionalized amino silanes is either through hydrosilation of a functionalized allyl amine, through reductive amination of a primary amino silane, or by nucleophilic substitution of gamma-chloropropyltrialkoxysilane. Unfortunately, functionalized allyl amines are not readily available, and are often quite expensive when they are available. Reductive aminations, on the other hand, are limited to symmetrical secondary amines, and often occur in such low yields that they are cost prohibitive, while nucleophilic substitution generates one equivalent of hydrochloride salt that must be recycled or disposed of.
Primary amines are one of the more reactive functional groups in organic chemistry and are known to react rapidly with a variety of carbonyl containing compounds. In the case of aldehydes and ketones, nucleophilic addition and dehydration results in an analogous imine structure that forms almost quantitatively at room temperature. Subsequent reduction of the imine functionality has been shown to provide an economical route to secondary amines. While the application of this methodology to amino silanes has already been reported in the patent literature, the direct reaction of silanes with aldehydes or ketones inevitably leads to the formation of siloxanes and lower yields.
The present invention overcomes the aforementioned problems by performing a water-producing condensation reaction between a carbonyl compound and a water-insensitive carrier amine, for instance butyl amine or aniline, to give an imine as the first intermediate adduct product; after removing water from the product and drying by conventional means, the carrier amine is then regenerated and recovered in an exchange reaction with a water sensitive aminoorganosilane to produce a second silyl imine intermediate adduct which is further reduced to either a secondary or tertiary amine depending on the nature of the aminoorganosilane.
The starting carbonyl compound may be a ketone, aldehyde, carboxylic acid or anhydride. In the case where the carbonyl compound is an aldehyde or ketone, the first and second intermediate adduct products are imines (i.e. aldimines and ketimines, respectively). Compounds which exist as aldehyde and ketone equivalents, e.g. ketals and acetals, may also be used to produce imine intermediates. In the case where the carbonyl compound is an anhydride or carboxylic acid, the resulting intermediate compounds are amides.
The use of secondary amino silanes as adhesion promoters is well known in urethanes and glass sizing agents. The conversion of silyl imines, produced by the process described above, to secondary amine can be accomplished under moderate hydrogen pressure and in the presence of a precious metal catalyst, i.e. Pd, Pt, Rh-containing catalysts, and the like. Other reduction methods for conversion of imines to secondary amines are also applicable and have been described in the prior art and are equally as applicable.
Using the method of the present invention, a whole new class of novel secondary amines, not possible using other methods, becomes available. In the case where an imine or imide of a volatilizable amine is already available, the first step of the process may be eliminated.
The second intermediate compounds, i.e. ketimino, aldimino and imido silanes, produced by the process of the invention have utility in their own right, as adhesion promoters, crosslinkers, as components of silicate clearcoats and the like. EP 976771, incorporated by reference herein in its entirety, describes a curable resin composition containing a curable resin and a ketimine structure-bearing organo-silicon compound that is useful as an adhesive. With respect to such compounds, therefore the final reduction step in the process described above may be eliminated.
The present invention herein also relates to the novel secondary and to novel second intermediate compounds, i.e. ketimino, aldimino and imido silanes, formed by the processes as described above.
The present invention provides a process whereby novel and valuable silyl imines or silyl imides having hydrolyzable groups bound to silicon can be produced and isolated. Silyl imines and imides produced by this method can be obtained in high yield and substantially siloxane-free. More particularly, the process of the invention provides product yields typically exceeding 90% and containing less than about 2 weight percent siloxanes. Moreover, subsequent reduction of the aforementioned imines provides a novel route to secondary and tertiary amines.
The steps of the invention are described in sequence, although as noted, the formation of the first intermediate may be eliminated if that product is available and the reduction to amine may be eliminated if the compound described herein as the second intermediate is the desired end product.
The process steps of the present invention can be practiced using either a batch mode process, or using a continuous process.
Step 1xe2x80x94Formation of First Intermediate Imine or Imide
The first step in the process of the invention involves a condensation reaction which forms an imine or imide from a water insensitive volatilizable primary amine (a xe2x80x9ccarrierxe2x80x9d amine) and a carbonyl compound. The imine forming condensation reaction may be represented by the following general reaction (I): 
In formula (I), R1 is a hydrocarbon group, suitably one having from 1 to 30 carbon atoms, although in principle even larger hydrocarbon groups may be employed as R1 groups, and may be an alkyl, aryl, alkaryl, aralkyl or alkarylalkyl group. Preferably, R1 has from 1 to 20 carbon atoms. R1 may also be an alkenyl or alkynyl group, although in such cases the final reduction step will likely hydrogenate some or all of the sites of aliphatic carbonxe2x80x94carbon unsaturation. R2 is hydrogen or a hydrocarbon group having from 1 to 20 carbon atoms, more preferably from 1 to 4 carbon atoms, and may be suitably an alkyl, aryl, alkaryl, aralkyl or alkarylalkyl group, or R1 and R2 together form a cyclic hydrocarbon group containing up to 8 carbon atoms. R3 is a hydrogen or a hydrocarbon group having from 1 to 10 carbon atoms, more preferably from 3 to 8 carbon atoms, and may be an alkyl, aryl, alkaryl, aralkyl or alkarylalkyl group, and n is 0 to 20, preferably 1 to 3.
In one specific embodiment of the reaction depicted above, R1 is benzyl, R2 is hydrogen and R3 is phenyl.
The primary carrier amines, R3NH2, useful herein include but are not limited to, allyl amine, ammonia, aniline, butyl amine, ethyl amine, isopropyl amine, tert-octyl amine, and so forth. Preferred amines are relatively low boiling, or are amines which will form a readily volatilizable azeotrope with a non-aqueous solvent such as toluene. Butylamine, which has a boiling point of about 76xc2x0 C., is an example of a preferred relatively low boiling amine. Aniline, which can be azeotropically distilled with toluene, is an example of an amine which is readily volatilizable with a non-aqueous solvent.
The condensation reaction (I) above may also be implemented starting with a compound which exists in equilibrium with an aldehyde or ketone, in particular an acetal, ketal, or an aldehyde-ammonia trimer.
Useful aldehydes include, but are not limited to, formaldehyde, acetaldehyde, butyraldehyde, hexanal, 2-ethyl hexanal, benzaldehyde, 1,4-terephthaldicarboxyaldehyde, glutaric dialdehyde, furfuraldehyde, and so forth. The aldehydes useful in carrying out the invention include difunctional aldehydes, such as difunctional terephthaldehyde, which ultimately result in production of difunctional amino silanes.
Useful ketones include, but are not limited to, cyclohexanone, acetone, butanone, acetophenone, and so forth.
Useful aldehyde-ammonia trimers include, but are not limited to, 2,4,6-trimethyl-1,3,5-hexahydrotriazine.
The carrier amine R3NH2 may also be reacted with an anhydride or carboxylic acid. In this instance, a silyl imide intermediate is formed in the subsequent Step 2, described hereinbelow, rather than a silyl imine intermediate. The reaction is illustrated by the condensation of an amine with succinic anhydride as depicted in equation (II): 
In equation (II), R3 is as previously defined.
The formation of succinimides is described in U.S. Pat. No. 5,145,984 and in U.S. Pat. No. 5,286,873, both of which are incorporated by reference herein in their entirety. Similarly, bisimide formation is described in EP 342 823, incorporated by reference herein in its entirety.
Again, as in the case of imine formation, when the amine reacts with the anhydride at room temperature, water is liberated. In the case where a di-carboxylic acid is used two moles acid are consumed in the reaction and two moles of water will be produced.
In the reaction of equation (II) any carboxylic acid or anhydride thereof may be used. Carboxylic acids having from 1 to 22 carbon atoms and their anhydrides are preferred.
Useful anhydrides include, but are not limited to, succinic anhydride, maleic anhydride, glutaric anhydride, acetic anhydride, propionic anhydride, and so forth.
Useful carboxylic acids include, but are not limited to, succinic acid, maleic acid, glutaric acid, acetic acid, propionic acid, butyric acid, and various fatty acids such as lauric, myristic, palmitic, steric and so forth.
In a specific embodiment of the present invention, the resultant imine is N-benzylidene aniline where R1 is phenyl, n is 1, R2 is hydrogen, and R3 is phenyl.
In another embodiment of the present invention, the resultant imine is N-cyclohexylidene butylamine where R1 and R2 are cyclohexyl, n is 0, and R3 is n-butyl.
The bulk water produced in the condensation reaction of an aldehyde or ketone with a primary amine can be removed by conventional means, such as phase separation with a separatory funnel or by azeoptropic distillation. Optionally, residual water can be removed using an inorganic dessicant such as sodium sulfate, magnesium sulfate, molecular sieves, and the like.
Step 2xe2x80x94Formation of Second Intermediate by Exchange with Silylalkylamine
The imine, or imide product of the first step, after drying, is then subjected to an exchange reaction with a primary aminoalkylsilane under anhydrous conditions to form a corresponding iminoalkylsilane or imidoalkylsilane. The carrier amine, R3NH2, used in step 1 is regenerated in this step and can be reused.
The reaction of the second step is illustrated for imines by the following equation (III): 
In equation (III), R1, R2, R3 and n are as previously defined, each R4 is independently hydrogen, a hydrocarbon group having from 1 to 8 carbon atoms, an alkoxy, or an acyloxy groups, and m is 2-20, preferably 3-5. Preferred R4 groups include hydrocarbon groups containing from 1 to 8 carbon atoms, more preferably from 1 to 3 carbon atoms. Some specific examples of R4 include, but are not limited to, methyl, ethyl, butyl, propyl, phenyl, benzyl, methoxy, ethoxy, butoxy, propoxy, and acetoxy.
Since the invention is particularly advantageous in the manufacture of water sensitive amino silanes it is preferred that at least one of the R4 groups, more preferably 2 or 3 of the R4 groups, are hydrolyzable alkoxy groups, for instance methoxy, ethoxy or isopropoxy, or acyloxy groups, for instance acetoxy. However, it should be understood that the invention can also be used to produce aminoalkylsilanes which are not water sensitive, such as where the R4 groups are all methyl groups.
Under similar conditions a primary aminoalkylsilane H2N(CH2)mSi(R4)3, will also exchange with an imide produced in the first step to give the corresponding imidoalkylsilane and regenerated carrier amine R3NH2.
Exemplary silanes which may be employed in this exchange reaction include gamma-amino propyl triethoxy silane sold under the tradename as Silquest A-1100 silane or gamma-amino propyl trimethoxy silane, sold under the tradename as Silquest A-1110 silane, both available from Crompton Corporation (Middlebury, Conn.).
The regenerated carrier amine R3NH2 is suitably removed under reduced pressure and recycled.
The iminoalkylsilanes and imidoalkylsilanes having at least one hydrolyzable alkoxy or acetoxy group thereon which are produced in this step are novel compounds which are useful as adhesion promoters, fiber sizing agents and the like. Consequently, if desired, the products of this exchange step may be isolated and used without being subjected to the third, reduction, step described below.
It should also be recognized that in the case where a suitable imide or imine is available from another source the first step in the process may be eliminated and the exchange reaction of this step may be performed directly on such an imide or imine. N-methyl succinimide and N-methylphthalimide are illustrative starting materials for this exchange step and can be obtained from a commercial source.
Step 3xe2x80x94Reduction to Silylamine
The silylalkylimine or silylalkylimide, produced as the second intermediate in the previous step can then be reduced to a corresponding aminoalkylsilane using methods and catalysts conventionally known to those of skill in the art. The reduction is depicted for second intermediate imine compounds in equation (IV), below: 
In equation (IV), R1, R2, R4, m and n are as previously defined.
In the case of reduction of an imidoalkylsilane as the second intermediate product, the carbonyl groups of the imidoalkylsilane may be reduced to give a tertiary aminoalkylsilane as illustrated by equation (V): 
In equation (V), R4 and m are as previously defined.
The reduction of this step can be accomplished in a variety of ways. For instance, see Tetrahedron Letters, Vol. 39(9), 1998, pages 1017-1020. Catalysts such as palladium on carbon, platinum on carbon, and so forth, have been successfully used.
While many methods have already been reported for the reduction of imines to amines, catalytic hydrogenation is the most economical. The catalysts useful in reducing the second intermediate imine to the corresponding amine include, but are not limited to, nickel, cobalt, platinum, palladium, rhodium, and so forth. Other reducing agents such as aluminum hydrides, borohydrides, hydrosiloxanes, and so forth, are also known and can be employed in this reduction step.
Bis- aminoalkysilane compounds can be produced using the method of the present invention, depending on the starting materials selected. For instance, the use of the difunctional aldehyde terephthaldehyde, results in bis-(aminoalkylsilyl)phenylene compounds.
The secondary and tertiary amino functionalized silanes of the present invention find utility as adhesion promoters and as coupling agents. For instance, the amines can be used as adhesion promoters in adhesives and sealants, and as coupling agents in compositions used in the plastics and glass-fibers industries and in foundries, in fabric treatment compositions, and in personal care products.
In particular, the secondary and tertiary amino functionalized silanes of the present invention are useful as coupling agents in the fiberglass and automotive glass industries.
Alternative Step 2(or step 1a)xe2x80x94Conversion of Imine to Tertiary Enamine
In some cases it may be desirable to produce a tertiary amine from a ketone or aldehyde starting compound. This can be accomplished if, in the starting aldehyde or ketone, R1(CH2)nC(xe2x95x90O)R2 used in the first step, n is at least 2. Tertiary amines can be produced from imines by the route of the following equation (VI): 
In equation (VI), R1, R2, R3, R4 and n are as defined previously. The invention is illustrated by the following non-limiting examples.